A smoke detector (i.e., a smoke alarm) is a device that detects (i.e., senses) smoke and issues a local audible or visual alarm in response to detecting smoke. Smoke detectors in large commercial, industrial, and residential buildings are typically powered by a central fire alarm system that is powered by building power with a battery backup. Domestic smoke detectors range from individual battery-powered units to several interlinked mains-powered units with battery backup.